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Yahoo has called a mystery press event in New York City on Monday afternoon, hot on the heels of rumors that it plans to buy Tumblr for US$1 billion.

"Join us as we share something special," says the invite, sent to members of the press Friday afternoon.

Citing unnamed sources, All Things D reported earlier Friday that Yahoo may be in talks to partner with Tumblr, invest in it, or make an outright purchase. It notes that Yahoo's CFO talked earlier this week about the need for Yahoo to bring back its "cool."

Adweek, in another report citing unnamed sources, put the value of the deal at $1 billion.

Marissa Mayer is expected to be at the New York City event, according to CNBC. Tumblr's headquarters are in New York.

The blogging and social network service was founded in 2007 and has 175 employees. It says it currently hosts more than 100 million blogs.